Crosslinked polyolefins are widely used in industrial applications, especially for the production of pipes, foams, insulator for wires and cables, domestic water pipelines, offshore oil and natural gas piping, and for the transportation of chemicals, slurries, sewage and the like.
Silanes are commonly employed as crosslinkers for the production of silane crosslinked polyolefins. The silane is typically used in conjunction with a peroxide, which is used to effect grafting of the silane onto the polyethylene. The silane containing polyolefin is then crosslinked in the presence of moisture and tin-based catalyst. Often, the silanes, peroxide, anti-oxidants and catalysts are mixed to form a silane composition which is stored prior to addition to the polyolefin. The silane, peroxide, anti-oxidants and catalysts composition are at a later time added to the polyolefin under conditions which affect the grafting of the silane to the polyolefin. Because the silane, peroxide, anti-oxidant and catalysts are stored prior to use, it is desirable to have a shelf-stable silane-graftable composition.
Silane crosslinking of polyolefins can lead to many improvements in various mechanical properties of the crosslinked polyolefin. But the resulting crosslinked polyolefin still contains the presence of tin and, during the cure, generate hazardous and/or volatile organic compounds, such as methanol. If silane crosslinking agents are used where the alkoxysilyl group is derived from higher boiling mono-alcohols, the curing times are often too long and impractical for the end-use application and therefore commercially not viable. Due to recent environmental concerns regarding the presence of tin compounds and the need to reduce hazardous air pollutants and volatile organic compounds during cure, it would be desirable to provide a way to crosslink polyolefins in the absence of tin and with reduced amounts of hazardous and volatile organic compounds produced during cure without compromising the resulting mechanical properties of the crosslinked polyolefin and still employing conventional equipment. It is also desirable that the silane graftable composition is shelf-stable.